Tactile feedback for indicating validity of communication link with an implantable medical device

ABSTRACT

Implantable medical device telemetry is provided between an implantable medical device and an external communication device. The implantable medical device includes a device transmitter and/or a device receiver. The external communication device includes a moveable communication head including an antenna therein connected to at least one of an external transmitter and/or an external receiver for communication with the device transmitter and/or the device receiver of the implantable medical device. A user moves the moveable head apparatus relative to the implantable medical device. Tactile feedback is provided to the user via the moveable head apparatus upon movement of the moveable head apparatus to a position where valid telemetry can be performed.

FIELD OF THE INVENTION

[0001] The present invention relates to communication links withimplantable medical devices. More particularly, the present inventionpertains to techniques for indicating that such communication links arevalid.

BACKGROUND OF THE INVENTION

[0002] In the field of implantable medical devices, such as cardiacpacemakers, tachyarrhythmia control devices, implantable drug dispensingdevices, monitoring devices, and nerve stimulators, it has become commonto provide a transceiver system for performing functions such as theremote programming and the telemetering of data out of the implanteddevice. For example, in such devices, it has become desirable to havethe ability to reprogram the device's modes of operation, parameters,and other functions and/or to monitor the performance of such devices,both historically and contemporaneously. Generally, such implantablemedical devices are designed to provide two-way telemetry by radiofrequency signal transmission between the implanted medical device and aprogramming head or wand of an external communication device, e.g.,external programmer apparatus, to provide for the exchange of codedtransmitted information therebetween.

[0003] As the complexity of implantable medical devices increases overtime, telemetry systems for enabling such implantable devices tocommunicate with external communication devices, e.g., programmers, hasbecome more important. For example, it is desirable for a user, e.g., aphysician, to noninvasively exercise some amount of control over theimplantable medical device, e.g., to turn the device on or off afterimplantation, to adjust various parameters of the implantable medicaldevice after implantation, etc.

[0004] Further, as implantable medical devices include more advancedfeatures, it is typically necessary to convey correspondingly moreinformation to the implantable medical device relating to the selectionand control of such advanced features. For example, if a pacemaker isselectively operable in various pacing modes, it is desirable that aphysician be able to noninvasively select a mode of operation. Further,for example, if a pacemaker is capable of pacing at various rates, or ofdelivering stimulating pulses of varying energy levels, it is desirablethat the physician be able to select, on a patient-by-patient basis,appropriate values for such variable operational parameters.

[0005] Not only has the complexity of implantable medical devices led tothe need to convey correspondingly more information to the implantablemedical device, but it has also become desirable to enable the implantedmedical device to communicate information outside of the patient to anexternal communication device, e.g., programmer. For example, fordiagnostic purposes, it is desirable for the implanted device to be ableto communicate information regarding its operational status to thephysician. Various implantable medical devices are available which cantransmit such information to an external communication device, e.g., thetransmission of a digitized ECG signal for display, storage, and/oranalysis by the external communication device.

[0006] As used herein, the term “uplink” and “uplink telemetry” will beused to denote the communications channel for conveying information fromthe implanted medical device to an external communication device, e.g.,a programmer. Conversely, the term “downlink” and “downlink telemetry”will be used to denote the communications channel for conveyinginformation from an external communication device to the implantedmedical device.

[0007] Various telemetry systems for providing the necessarycommunication channels between an external communication device and animplanted medical device have been described. For example, typically,telemetry systems are employed in conjunction with an externalprogrammer/processing unit. A programmer for noninvasively programming acardiac pacemaker is described in the following U.S. Patents toHartlaub, et al., each commonly assigned to the assignee of the presentinvention: U.S. Pat. No. 4,250,884, entitled “Apparatus for and Methodof Programming the Minimum Energy Threshold for Pacing Pulses to beApplied to a Patient's Heart;” U.S. Pat. No. 4,273,132, entitled“Digital Cardiac Pacemaker with Threshold Margin Check;” U.S. Pat. No.4,273,133, entitled “Programmable Digital Cardiac Pacemaker with Meansto Override Effects of Reed Switch Closure;” U.S. Pat. No. 4,233,985,entitled “Multi-Mode Programmable Digital Cardiac Pacemaker;” U.S. Pat.No. 4,253,466, entitled “Temporary and Permanent Programmable DigitalCardiac Pacemaker;” and U.S. Pat. No. 4,401,120, entitled “DigitalCardiac Pacemaker with Program Acceptance Indicator.” Aspects of theprogrammer that are the subject of the foregoing Hartlaub et al. patentsare described in U.S. Pat. No. 4,208,008 to Smith, entitled “PacingGenerator Programming Apparatus Including Error Detection Means,” and inU.S. Pat. No. 4,236,524 to Powell et al., entitled “Program TestingApparatus.”

[0008] Most commonly, telemetry systems for implantable medical devicesemploy a radio frequency (RF) transmitter and receiver in theimplantable medical device, and a corresponding RF transmitter andreceiver in the external communication device, e.g., programming unit.Within the implantable medical device, the transmitter and receiver usean antenna for receiving downlink telemetry signals and for radiating RFsignals for uplink telemetry. For example, the radiating RF signals maybe magnetically coupled through inductive (antenna) coils.

[0009] To communicate digital data using RF telemetry, a digitalencoding scheme such as described in U.S. Pat. No. 5,127,404 to Wybornyet al., entitled “Improved Telemetry Format,” is used. In particular,for example, in downlink telemetry a pulse interval modulation schememay be employed wherein the external communication device, e.g.,programmer, transmits a series of short RF “bursts” or pulses in whichthe duration of an interval between successive pulses, e.g., theinterval from the trailing edge of one pulse to the trailing edge of thenext pulse, encodes the data. For example, a shorter interval may encodea “0” bit while a longer interval may encode a “1” bit.

[0010] The external communication devices, e.g., programming devices,typically interface with the implanted medical device through the use ofa programming head or paddle. For example, generally, the programminghead or paddle is a hand-held unit adapted to be placed on or near thepatient's body over the implant site of the patient's implanted medicaldevice. The programming head may effect closure of a reed switch in theimplantable medical device using a magnet to initiate a telemetrysession. Thereafter, uplink and downlink communication may take placebetween the implanted medical device's transmitter/receiver and thereceiver/transmitter of the external communication device. Other methodsof initiating a telemetry session may also be used. For example, awake-up pulse from an external communication device may be used towake-up the implanted medical device which polls its downlink receiverat an appropriate interval.

[0011] For programming arrangements, and/or for monitoring arrangements,both uplink and downlink telemetry signal strength vary as a function ofprogramming head positioning relative to the implantable device. Inother words, the signal strength varies as a function of the coefficientof coupling between the communication head, e.g., programming headincluding an antenna configuration, and the implanted device. Therefore,it is important for the programming head to be properly positioned overthe patient's implant site so that downlink RF signals can be detectedin the implantable medical device and uplink signals can be detected bythe programming head of the external communication device. For example,if the programming head is too far away from the implantable medicaldevice, the attenuation of RF signals transmitted across the boundary ofthe patient's skin may be too great, preventing a telemetry link frombeing established.

[0012] As such, with appropriate feedback to a user, the user canposition and reposition the programming head over the implant site untila suitable position is located to a establish a valid communication linkbetween the external communication device and the implanted medicaldevice. Various feedback techniques have been used to indicate to a userwhen a programming head has been properly located over a patient'simplanted medical device to establish a valid telemetry link.

[0013] For example, one technique used for determining when theprogramming head is properly positioned can be characterized as an “openloop” technique in that the determination of the correct headpositioning is based solely upon an assessment of whether the uplinksignal (i.e., the signal transmitted from the implanted medical deviceto the external communication device) meets some minimum requirement. Insuch an open loop verification system, adequate downlink signal strengthis not tested. For example, an open loop system for determining theproper positioning of a programming head is described in U.S. Pat. No.4,531,523 to Anderson, entitled “Digital Gain Control for the Receptionof Telemetry Signals from Implanted Medical Devices.”

[0014] A communication protocol using handshaking can also be used toverify that a minimum downlink field strength for detection in theimplanted medical device exists to signal a physician that correct headpositioning has been achieved. However, conventional handshakingprotocols do not provide any information useable for optimization ofhead positioning to ensure an adequate operating margin. In other words,proper programming head positioning may be indicated even though theprogramming head is actually marginally positioned, such that a veryslight shift in positioning (e.g., due to patient motion) results indownlink telemetry failure.

[0015] Further, closed loop systems have also been described forproviding feedback to a user for positioning of the communication headfor attaining a valid communication link with an implanted medicaldevice. For example, in U.S. Pat. No. 5,324,315 to Grevious, entitled“Closed-Loop Downlink Telemetry and Method for Implantable MedicalDevice,” a specific type of downlink telemetry pulse is transmitted fromthe external communication device to the implanted medical device. Inparticular, the downlink pulses are bursts having a linear-rampingenvelope. The characteristics of the downlink burst envelope are suchthat the amplitude of the signal as detected by the implanted medicaldevice's receiver, relative to the receiver's detection threshold, canbe ascertained by measuring the time that the detected burst exceeds thereceiver's detection threshold. This information can be communicated tothe external communication device. In response to receipt of suchinformation regarding the relative strength of the detected downlinksignals, the external communication device can modulate the peakamplitude of the downlink burst envelopes by modulating the gain of theexternal communication device transmitter. As such, the externalcommunication device can then ensure an adequate margin over theimplanted medical device's detection threshold while at the same timeavoiding the transmission of unnecessarily high energy downlink signals.As described therein, the downlink signal strength and/or the uplinksignal strength can be used for activation of a telemetry statusindication.

[0016] Generally, as described in U.S. Pat. No. 5,324,315, the provisionof feedback as to the proper positioning of a programming head withrespect to an implanted antenna of an implanted medical device includesthe use of a position indicator, for example, an audible tone generatorand/or a visible indicator such as a light emitting diode (LED). Whensignal strength and accuracy are confirmed (e.g., with parity checking,error checking codes, and the like), programmer control circuitry willcause the position indicator to indicate that a link has beenestablished. If adequate signal strength and content accuracy cannot beconfirmed, the position indicator will so indicate.

[0017] Further, U.S. Pat. No. 5,107,833 to Barsness, entitled “TelemetryGain Adjustment Algorithm and Signal Strength Indication in a NoisyEnvironment,” describes provision of a signal strength indicator forproviding the user with a visual alpha-numeric readout of signalstrength during establishment of a telemetry link. The signal strengthis derived from an automatic gain control factor of an adjustable gainamplification stage of an external communication device, e.g., theadjustable gain amplification stage of the uplink receiver of aprogrammer which receives its input signals from an RF programming headhaving an antenna configuration therein. The gain of the uplink receiveris a function of the strength of the uplink signal. As describedtherein, with a telemetry session initiated and uplink signal lossoccurring for performing telemetry, the automatic gain controlalgorithms scan through gain levels searching for one which will resultin valid uplink detection. A displayed range of signal strengthscorrespond to the scaled automatic gain control levels or factors. Sincethe automatic gain control value is lowest for maximum signal level andhighest for minimum signal level, the value is complemented for use as asignal strength indicator to the user. As described therein, variouslevels of automatic gain control could be used. For example, scaledvalues of 0-100, or values of 0-9, may be used for display to a userattempting to position the programming head. The signal strengthindicator may appear on a screen of a programmer or it could appear onthe programming head as a numeric display for the user to view as theuser attempts to find an optimum position for the programmer head basedon the viewed strength signal indication.

[0018] Further, programmer heads available under the trade designation9766/9766A/9767, available from Medtronic, Inc., assignee of the presentinvention, provide for a multiple LED array display for providingindication of proper positioning of the programmer head. The array isdriven as a function of the uplink signal strength. The signal strengthis determined as a function of the gain of the uplink receiver. Acertain number of LEDs of the LED array are activated based upon thesignal strength. For example, when the head is not at an optimumposition, only one LED may be lit. As the programmer head is movedaround the site of the implanted medical device, more LEDs may be litindicating more optimal positions. Further, no LEDs of the array may belit until valid telemetry can be accomplished, i.e., as determined by ahandshake process.

[0019] As described above, conventional RF heads incorporate varioustypes of indicators to guide placement of the RF head. For example, the9766 family of RF heads available from Medtronic Inc., assignee of thepresent invention, incorporate signal strength indicator LEDs to guideplacement of the RF head. Further, other positioning techniques haveused numerical displays for indicating the signal strength to a user toguide placement of the RF programmer head. However, in brightly litrooms, LEDs or visual numerical displays are sometimes difficult to seeand/or read. As such, these indicators are inadequate for optimalplacement of an RF programmer head.

[0020] Further, in some circumstances, implantable medical devices areimplanted in various regions of the body which prohibit the viewing ofan RF programmer head as it is placed over the implant site. Forexample, neurostimulators are sometimes implanted in the hip area. Assuch, when a programming head of an external communication device isplaced for performing telemetry over the implant site, the user of thehead may find it difficult to view LEDs on the head.

[0021] SUMMARY OF THE INVENTION

[0022] The present invention provides for the use of tactile feedback inconjunction with the positioning of a communication head for performingtelemetry between an implantable medical device and an externalcommunication device. Tactile feedback allows a user to locate animplanted device with a communication head without looking at anindicator light, a numeric display, etc.

[0023] An implantable medical device telemetry method according to thepresent invention includes providing an implantable medical device andan external communication device. The implantable medical deviceincludes a device transmitter and/or a device receiver. The externalcommunication device includes an external transmitter and/or an externalreceiver connected to an antenna for communication with the devicetransmitter and/or the device receiver. The method further includesdetermining validity of a communication link between the devicetransmitter and/or the device receiver of the implantable medical deviceand the external transmitter and/or the external receiver of theexternal communication device. Tactile indication is provided as afunction of the validity determination.

[0024] In one embodiment of the method, the external communicationdevice includes a user communication head moveable relative to theimplantable medical device when the implantable medical device isimplanted. The tactile indication is provided to a user via the usercommunication head.

[0025] In another embodiment of the method, the validity of thecommunication link is determined by detecting communication of a signalbetween the implantable medical device and the external communicationdevice. The strength of the communicated signal is determined and thestrength of the communicated signal is compared to at least onepredetermined reference strength.

[0026] Further, with regard to this embodiment, a tactile indication maybe provided by controlling the frequency of vibration of the tactileindication as a function of the strength of the communicated signal.

[0027] In another embodiment of the method, determining the validity ofa communication link includes completing a handshake between the devicetransmitter and/or the device receiver of the implantable medical deviceand the external transmitter and/or the external receiver of theexternal communication device.

[0028] In yet another embodiment of the method, providing the tactileindication as a function of the validity determination may includeinitiation of the tactile indication upon determination of a validcommunication link. Further, with regard to this particular embodiment,the tactile indication may be discontinued after a predetermined timefollowing initiation thereof. Yet further, activation of an indicatormay be provided when the valid communication link becomes invalidfollowing such discontinuation of the tactile indication.

[0029] In yet another embodiment, the tactile indication as a functionof the validity determination is provided by continuously providingtactile indication during the entire period of time that a validcommunication link is determined.

[0030] Another implantable medical device telemetry method according tothe present invention includes providing an implantable medical deviceand an external communication device. The implantable medical deviceincludes a device transmitter and/or a device receiver. The externalcommunication device includes a moveable head apparatus including atleast an antenna therein connected to at least one of an externaltransmitter and/or an external receiver for communication with thedevice transmitter and/or the device receiver of the implantable medicaldevice. The method further includes moving, by the user, the moveablehead apparatus relative to the implantable medical device. Tactileindication is provided to the user via the moveable head apparatus uponmovement of the moveable head apparatus to a position where informationbetween the device transmitter and/or the device receiver of theimplantable medical device and the external transmitter and/or externalreceiver of the external communication device is communicated.

[0031] An implantable medical device telemetry system is also describedaccording to the present invention. The system includes an implantablemedical device including a device transmitter and/or a device receiverand an external communication device. The external communication deviceincludes an external receiver and/or an external transmitter connectedto an antenna for communication with the device transmitter and/or thedevice receiver. The external communication device further includes atactile feedback generation device and control circuitry operable toinitiate the tactile feedback generation device as a function of thevalidity of a communication link between the implantable medical deviceand the external communication device.

[0032] In one embodiment of this system, the external communicationdevice includes a user communication head moveable relative to theimplantable medical device when the implantable medical device isimplanted. Further, the tactile feedback generation device and theantenna of the external communication device are provided within themoveable user communication head.

[0033] In various embodiments of the system, the tactile feedbackgeneration device may include a vibrating motor, a piezoelectric device,an electric solenoid, or a relay contact.

[0034] A communication device for establishing a communication link withan implantable medical device is also described. The device includes anexternal receiver and/or an external transmitter connected to an antennafor communication with a device transmitter and/or a device receiver ofthe implantable medical device. The communication device furtherincludes a tactile feedback generation device and control circuitryoperable to initiate the tactile feedback generation device as afunction of the validity of a communication link between the implantablemedical device and the external communication device.

[0035] The above summary of the present invention is not intended todescribe each embodiment or every implementation of the presentinvention. Advantages, together with a more complete understanding ofthe invention, will become apparent and appreciated by referring to thefollowing detailed description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a diagram illustrating an implantable medical device ina body for communication with an external communication device, whereinthe implantable medical device and external communication device providetelemetry with use of tactile feedback according to the presentinvention.

[0037]FIG. 2 is a general block diagram of circuitry of an implantablemedical device including transmitter and receiver circuitry according tothe present invention.

[0038]FIG. 3 is a general block diagram of an illustrative telemetrysystem using tactile feedback according to the present invention.

[0039]FIG. 4 is one embodiment of a portion of the illustrative externalcommunication device shown generally in FIG. 3 according to the presentinvention.

[0040]FIG. 5 is a more detailed diagram of one illustrative embodimentof a portion of the external communication device shown in FIG. 4according to the present invention.

[0041]FIG. 6 is one illustrative embodiment of a tactile feedbackgeneration device according to the present invention.

[0042]FIG. 7 is a general block diagram of a head positioning methodillustrating tactile feedback according to the present invention.

[0043] FIGS. 8A-8C show various illustrative embodiments of the generalhead positioning method illustrating tactile feedback as shown in FIG.7.

[0044]FIG. 9 is a block diagram of one illustrative embodiment of ahandshake used according to the present invention for determiningvalidity of a communication link.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045]FIG. 1 shows a telemetry system 10 according to the presentinvention. The telemetry system 10 includes implantable medical device12 and external communication device 15 which are operable forestablishing a communication link 16 therebetween. Preferably, theexternal communication device 15 includes a controller apparatus 32,e.g., a programmer apparatus, having a communication head 30electrically coupled thereto. The controller apparatus 32 interfaceswith the implantable medical device through the use of the communicationhead 30, e.g., a programming head or paddle. For ease of use, theprogrammer head 30 is connected to other components of the programmerapparatus 32 via a cable, e.g., a straight or coiled cable, althoughwireless communication or any other electrical connection is possible.

[0046] Generally, the communication head 30 is a hand-held unit adaptedto be placed on or in close proximity to the patient's body over theimplant site of the patient's implanted medical device 12 to establishthe communication link 16. Preferably, according to the presentinvention, the communication head 30 includes tactile feedback (alsoreferred to herein as tactile indication) to provide a user withinformation as to the proper positioning of the communication head 30relative to the implantable medical device 12.

[0047] Although the present invention is described herein with respectto tactile indication or feedback being provided via the hand-heldcommunication head 30, such tactile indication may be provided to theuser by any other suitable apparatus. For example, the tactile feedbackmay be provided via a device located proximate another portion of theuser's body such as a wearable wristband, an apparatus attachable to auser's pocket or other portions of clothing, or any other apparatuscapable of providing tactile indication to the user. As used herein,tactile indication or tactile feedback refers to any feedbackperceivable by a user's sense of touch, e.g., vibratory motiontransmitted to the housing of the communication head 30 and therefore toa user's hand holding the hand-held communication head 30, or any othermotion perceivable by the user's sense of touch.

[0048] As shown in FIG. 1, implantable medical device 12 is implanted inbody 18. Implanted device 12 includes a housing 13 in which componentsof the implantable medical device 12 are hermetically sealed, e.g.,pacing circuitry, defibrillation circuitry, a battery, monitoringcircuitry, etc. Also positioned within the housing 13 istransmitter/receiver circuitry 70, as shown in FIGS. 2 and 3. Asillustratively shown in FIG. 1, at least one lead 14 is connected to theillustrative implantable medical device 12 in connector block region 17such as with the use of feedthrough(s) (not shown). For example, theimplantable medical device 12 may be implanted near a human heart 11. Inthe case where the implantable medical device 12 is an illustrativepacemaker implanted in the body 18, the pacemaker may include a pacingand sensing lead represented generally as lead 14 to sense electricalsignals attendant to the depolarization and repolarization of the heart11, and to provide pacing pulses for causing depolarization of cardiactissue in the vicinity of the distal ends thereof.

[0049] Implantable medical device 12 may be any implantable medicaldevice embodying transmitter/receiver circuitry as described herein. Forexample, in the case where the implantable medical device is apacemaker, the implantable device may be, for example, a pacemaker suchas that described in U.S. Pat. No. 5,158,078 to Bennett, et al.; U.S.Pat. No. 5,312,453 to Shelton et al.; or U.S. Pat. No. 5,144,949 toOlson et al.

[0050] Implantable medical device 12 may also be apacemaker-cardioverter-defibrillator (PCD) corresponding to any of thevarious commercially-available implantable PCDs. For example, thepresent invention may be practiced in conjunction with PCDs such asthose described in U.S. Pat. No. 5,545,186 to Olson, et al.; U.S. Pat.No. 5,354,316 to Keimel; U.S. Pat. No. 5,314,430 to Bardy; U.S. Pat. No.5,131,388 to Pless; or U.S. Pat. No. 4,821,723 to Baker, et al.

[0051] Alternatively, implantable medical device 12 may be animplantable neurostimulator or muscle stimulator such as that disclosedin U.S. Pat. No. 5,199,428 to Obel, et al.; U.S. Pat. No. 5,207,218 toCarpentier, et al.; or U.S. Pat. No. 5,330,507 to Schwartz, or animplantable monitoring device such as that disclosed in U.S. Pat. No.5,331,966 to Bennett, et al.

[0052] Further, for example, the implanted device 12 may be acardioverter-defibrillator, a brain stimulator, a gastric stimulator, adrug delivery device, a hemodynamic monitoring device, or any otherimplantable device that would benefit from telemetry capabilitiesaccording to the present invention using tactile feedback. Therefore,the present invention is believed to find wide application. As such, thedescription herein making reference to any particular medical device isnot to be taken as a limitation of the type of medical device which maybe used in association with the tactile feedback of externalcommunication device 15 according to the present invention.

[0053]FIG. 2 generally illustrates a high level block diagram ofconstituent components of one embodiment of implantable medical device12, where the medical device is implemented with a microprocessor-basedarchitecture. However, the electronic features and operations of theimplantable medical device 12 may be implemented in discrete logic or asa microcomputer-based system. As shown in FIG. 2, the implantablemedical device 12 includes a microcomputer circuit 42 including at leasta processor 46 and memory 48. The microcomputer circuit 42 is coupled bya data communication bus 50 to a controller circuit 52 of aninput/output circuit 40. For example, microcomputer circuit 42 may forma custom integrated circuit device augmented by standard RAM/ROMcomponents.

[0054] Further, for example, the input/output circuit 40 may include anyother number of circuits in addition to the controller 52 such as isnecessary for accomplishing the function of the implantable medicaldevice 12. For example, the input/output circuit 40 may include senseamplifiers, peak sense and threshold measurement units, bias circuits,pulse generators, threshold detectors, etc., along with otherinput/output circuits such as those required to provide the controller52 with appropriate signaling information. The specific embodiments ofsuch circuits are not critical to the practice of the present inventionso long as the circuits provide for generating signals corresponding tothe desired implantable medical device and/or are capable of providingcontroller 52 with signals indicative of applicable physiologicalevents, e.g., natural and stimulated contractions of the heart, and alsoso long as the implantable medical device 12 includestransmitter/receiver circuitry 70 according to the present invention foruse in a telemetry system 10 as described herein.

[0055]FIG. 3 is a block diagram of the telemetry system 10 including theimplantable medical device 12 such as described above with reference toFIG. 2 and the external communication device 15. A dashed line 21represents the boundary (e.g., the patient's skin) between the implantedmedical device 12 and external communication device 15.

[0056] As described above, the implantable medical device 12 includes atleast transmitter/receiver circuitry 70 for establishing a communicationlink with external communication device 15. Transmitter/receivercircuitry 70, including transmitter circuit 72 and receiver circuitry70, is coupled to antenna 19. Although the transmitter/receivercircuitry 70 is shown to include only transmitter circuit 72 andreceiver circuit 74, other circuitry for controlling such transmitterand receiver circuits 72, 74 also form a part of implantable medicaldevice 12, e.g., processors for controlling wake-up functions,controlling flow of data to the transmitter for modulation on a carriersignal, etc. In addition, other components of the implantable device 12,e.g., battery, provide power to such circuitry. The antenna 19 may be ofany antenna type utilized in implantable medical device applications fortelemetry functions, e.g., multi-turn wire coil antennas.

[0057] The transmitter/receiver circuitry 70 generates modulatedelectrical signals for provision to an antenna 19 such thatelectromagnetic waves are radiated. An antenna 64 associated with thecommunication head 30 receives the electromagnetic waves from theimplanted medical device 12. Transmitter/receiver circuitry 60 of theexternal communication device 15 receives and demodulates the modulatedelectrical signals induced in the antenna 64 representative of theelectromagnetic waves radiated from the antenna 19 of the implantablemedical device 12.

[0058] Generally, the external communication device 15 is an apparatushaving at least transmitter/receiver circuitry 60 and an antenna 64 fortransmitting and receiving electromagnetic energy. Further, the externalcommunication device 15 includes control circuitry 80 (e.g., processor,software 84, memory, etc.) connected for control of telemetrytransceiver circuitry 60. The external communication device 15 may beany programmer such as those used in telemetry systems for receivinginformation from an implantable medical device 12 and transmittinginformation thereto. Generally, as previously described herein, suchprogrammers are used to adjust parameters of implantable medical devicesand typically have graphic displays, keyboards, or other user interfacesfor data entry and device control by operator manipulation. Further,such programmers generally include printers or plotters to allow theuser to control, evaluate, and document the extensive capabilities ofthe implanted device 12 from which it is receiving information.

[0059] For example, external communication device 15 may include variousdevices available from Medtronic, Inc., assignee of the presentinvention. For example, such devices may include programmers operablewith communication heads available from Medtronic, Inc. such as a 9790programmer operable in conjunction with RF heads including thoseavailable from Medtronic, Inc. under the trade designation 9766 RFHeads, 9766A RF Heads, and 9767 RF Heads; and a Medtronic 2090programmer which is operable with a 9767 RF Head. Further, the devices15 may include patient activators, e.g., patient activated devices forfreezing memory recordings, such as a Medtronic 9462 patient activator;Medtronic 9464 patient activator; or a Medtronic 6190 or 6191 patientactivator. Yet further, the device 15 may be a neurostimulatorprogrammer such as those available under the trade designation Medtronic7432 programmer, Medtronic 3425 programmer, Medtronic 3210 programmer;or a drug delivery device programmer available under the tradedesignation Medtronic 8820 programmer which is operable with a 9766 RFhead. Each of such devices may be modified according to the presentinvention to provide tactile feedback to a user when attempting toestablish a communication link between the implantable medical device 12and the external communication device 15.

[0060] The transmitter/receiver circuitry 60 of external communicationdevice 15 generates modulated electrical signals for provision toantenna 64 of the communication head 30 such that electromagnetic wavesare radiated. The antenna 19 associated with the implantable medicaldevice 12 receives the electromagnetic waves from the externalcommunication device 15. The transmitter/receiver circuitry 70 of theimplantable medical device 12 receives and demodulates the modulatedelectrical signals induced in the antenna 19 representative of theelectromagnetic waves radiated from the antenna 64 of the externalcommunication device 15.

[0061] As would be known to one skilled in the art, the transceivercircuitry 60 of the external communication device 15 includes receivercircuitry 62 that is compatible with the transmitter 72 of the implantedmedical device 12 and operable for receiving and demodulating thetransmitted signal therefrom. Further, the transceiver circuitry 60 ofexternal communication device 15 includes transmitter circuitry 61 thatis compatible with the receiver 74 of the implanted device 12 andoperable for generating a modulated signal of which the receiver of theimplanted medical device 12 is capable of receiving and demodulating.The transceiver circuitry 60 is coupled to antenna configuration 64 forcommunicating with the implantable medical device 12 via antenna 19.

[0062] Antenna 64 is preferably disposed within hand-held communicationhead 30 surrounded by a housing 31 generally represented by dashed linein FIG. 3. The hand-held communication head 30 can then be convenientlyplaced in proximity to the patient's implant site. When so positioned,antenna 64 receives uplink telemetry signals transmitted from implantedmedical device antenna 19 and transmits downlink telemetry signals to bereceived by implanted medical device antenna 19 as indicated by thedouble-arrowed communication link 16.

[0063] It will be readily apparent to one skilled in the art from thedescription herein that the present invention need not be used as abi-directional telemetry system, but may be used as a unidirectionalsystem. In other words, external communication device 15 may onlyinclude a receiver to receive information from a transmitter ofimplantable medical device 12. For example, this may be the case in animplantable monitoring device. Likewise, external communication device15 may only include a transmitter for transmitting information to areceiver of the implantable medical device 12. This may be the casewhere implantable medical device 12 is only being programmed by theexternal communication device 15.

[0064] To provide feedback as to the proper positioning of thecommunication head 30 relative to the implanted medical device antenna19 to establish a valid communication link, tactile feedback generationdevice 90 is provided according to the present invention. Unlikeconventional indicator devices, tactile feedback generation device 90allows a user to locate an implantable medical device 12 using thecommunication head 30 without the requirement of looking at an indicatorlight. However, as further described below, other indicators may be usedin conjunction with the tactile feedback generation device 90. Forexample, a position indicator or telemetry status indicator 86 may beused in conjunction with the tactile feedback to properly position theexternal antenna 64 relative to the implanted medical device antenna 19,e.g., the telemetry status indicator may be activated after a handshakeis performed and confirmation thereof is attained indicating that at avalid communication link has been established at a certain communicationhead position, while tactile feedback may be used to indicate a moreoptimal position for the communication head 30.

[0065] The use of tactile feedback in positioning the communication head30 for performing telemetry according to the present invention shall befirst generally described with reference to the general head positioningmethod 100 of FIG. 7 and then various illustrative embodiments of such ageneral method shall be described with reference to FIGS. 8A-8C. Headpositioning method 100 generally includes the initiation of a telemetrysession as shown in block 102. For example, a telemetry session may beinitiated by the closing of a reed switch of an implantable medicaldevice 12 as is known in the art, may be initiated by a wake-up pulse,or may be initiated by any other technique for beginning a telemetrysession. Thereafter, telemetry is attempted (block 103) under control ofcontrol circuitry 80. It is then determined whether valid telemetry hasbeen accomplished (block 104) or, in other words, whether a validcommunication channel or link is established between the implantablemedical device 12 and the external communication device 15. If such avalid telemetry link is not determined, then no tactile feedback isprovided to the user. As such, the user knows that the usercommunication head 30 must be moved relative to the implanted device 12.Further communication between the implantable medical device 12 and theexternal communication device 15 is then attempted with thecommunication head 30 in a new position. Once valid telemetry isachieved, tactile feedback is activated (block 106) based on thetelemetry validity determination (block 104).

[0066] One skilled in the art will readily recognize that varioustechniques may be used for determining valid telemetry (block 104). Forexample, valid uplink telemetry may be determined, valid downlinktelemetry may be determined, bi-directional valid telemetry may bedetermined, signal strength may be used for determining valid telemetry,handshaking may be used to determine valid telemetry, CRC checking orerror checking may be used to determine valid telemetry, or any otherprocesses or combination of processes for determining that a channel isvalid may be used according to the present invention.

[0067] Further, one skilled in the art will recognize that tactilefeedback may be used in different manners to indicate valid telemetryunder different circumstances or different applications. For example,tactile feedback may be used upon initial detection of a validcommunication channel even though the communication head may not be at aposition that provides a signal of optimum strength; tactile feedbackmay be used only upon finding a communication head position thatprovides a telemetry signal of a particular strength as determined by apredetermined reference strength level; tactile feedback may be used toindicate an initial detection of a valid communication channel with thetactile feedback being modified as a function of signal strength aspositions providing greater or lesser signal strength are located; etc.

[0068] FIGS. 8A-8C are provided to illustrate several embodiments of thegeneral head positioning method 100 described above with reference toFIG. 7. As shown in FIG. 8A, head positioning method 120 includestelemetry initiation (block 121). For example, as described above, atelemetry session may be initiated by the closing of a reed switch of animplantable medical device 12 as is known in the art, may be initiatedby a wake-up pulse, or may be initiated by any other technique forbeginning a telemetry session. Thereafter, telemetry is attempted (block123) such as by starting a handshake protocol. For example, afterinitiation of the telemetry session (block 121), a handshake sequencemay be periodically performed to establish and/or continually assess avalid telemetry link.

[0069] Generally, the handshake protocol includes carrying out ahandshake sequence that includes a handshake request, a window of timefor a response to the request, and a handshake confirmation. One skilledin the art will recognize that either the implantable medical device 12or the external communication device 15 may be used to initiate thehandshake sequence with a handshake request. Preferably, the handshakesequences are initiated by a handshake request from the implantablemedical device 12. For example, the handshake protocol may be performedin a manner such as that described in U.S. Pat. No. 5,292,343 toBlanchette, et al., entitled “Handshake for Implanted Medical DeviceTelemetry.”

[0070]FIG. 9 shows one illustrative embodiment of a handshake procedure246 which may be used in conjunction with the telemetry system 10. Oneskilled in the art will recognize that various handshake sequences andtechniques may be used to determine a valid communication channelbetween the implantable medical device 12 and the external communicationdevice 15. As such, the present invention is not limited to anyparticular handshake sequence or technique. It will be furtherrecognized that handshake sequences are periodically carried out duringan initiated telemetry session to determine that a link is still validas well as at the beginning of a telemetry session to determine theestablishment of a valid communication channel.

[0071] As shown in FIG. 9, the illustrative handshake procedure 246 isinitiated at handshake block 148. The implantable medical device 12transmits the handshake request (block 250). If the externalcommunication device 15, e.g., programmer, receives the handshakerequest as determined at block 252, then external communication device15 (e.g., programmer) transmits a handshake reply (block 253) during ahandshake reply window. If the programmer 15 does not receive thehandshake request, a time-out period is issued so as to continue waitingfor the handshake request (block 255). If, during the time-out, externalcommunication device 15 receives a handshake request, a handshake reply(block 253) is issued. Block 256 illustrates that some time during thetime-out is expended by the implanted medical device 12 in waiting forthe handshake reply. If during the time-out no handshake reply isreceived by the implanted medical device 12 indicating that thehandshake request was not received by external communication device 15,a handshake failure (block 258) is issued and the handshake sequence isexited (block 260) until the next periodic handshake sequence. Aproperly timed reply during the reply window from the externalcommunication device 15 received by the implantable medical device 12(block 254) causes transmission of a handshake confirmation (block 262).

[0072] As shown in FIG. 8A, upon completion of the handshake sequence,if a confirmation was not received, then further communication isattempted, e.g., another handshake is attempted (block 123). On theother hand, if the handshake is confirmed (block 122), then optionally,a visual or audible indicator is provided (block 126) and, according tothe present invention, tactile feedback may be also activated (block124). The optional indication shown by block 126 in FIG. 8A is alsoillustrated in FIG. 9. For example, as shown in FIG. 9, upon receipt ofthe confirmation (block 264) by the external communication device 15, anindication that a link is established may be provided, e.g., an LED isextinguished (block 266). Likewise, an indication that the confirmationwas not received may also be indicated in some manner, e.g., an LED islighted (block 268). Thereafter, the handshake sequence is exited (block270).

[0073] Although tactile feedback may be provided in response to aconfirmed handshake as described above which indicates a validcommunication channel to the user, tactile feedback may be inhibiteduntil a determination has been made that the telemetry signal strengthmeets a predetermined reference level. This determination is furtherdescribed below with reference to FIG. 8B.

[0074] Further, as shown in FIG. 8A, in addition to the activation oftactile feedback upon confirmation of a valid handshake, the tactilefeedback may be adjusted as a function of the telemetry signal strength(block 124). The signal strength (block 128) is provided such that thetactile feedback may be activated as a function thereof. For example,the frequency of vibration may be increased as signal strength (block128) is increased. Likewise, the frequency of vibration of the tactilefeedback may be decreased upon a decrease in signal strength (block128). In such a manner, the user is provided with a varied tactilefeedback as a function of the signal strength such that optimumpositioning of the head 30 can be attained by the user. For example, theuser may move the handheld communication head 30 to the position wheretactile feedback having the high frequency of vibration is sensed. Withthe communication head 30 properly positioned, telemetry is completed(block 129).

[0075] Signal strength may be determined by any number of differenttechniques. Such signal strength may be representative of uplink signalstrength, downlink signal strength, or a combination of uplink anddownlink signal strength. For example, when uplink telemetry signals arereceived by antenna 64 and uplink receiver 62, the strength of thereceived signals can be assessed or monitored based upon the gainsetting of the uplink receiver 62. Such monitoring of the gain is, forexample, described in U.S. Pat. No. 5,107,833 to Barsness and U.S. Pat.No. 5,324,315 to Grevious. Generally, the gain of the uplink receiver 62is inversely proportional to the signal strength. For example, a lessersignal strength results in a higher gain being provided by the receiver62, and a higher signal strength results in a lesser gain being providedby receiver 62.

[0076]FIG. 8B illustrates another alternate embodiment of a headpositioning method 130. The head positioning method 130 includesinitiating telemetry (block 131) in a like manner as described withreference to FIG. 8A. Likewise, as shown in block 133, telemetry isattempted and a handshake sequence 132 is performed. Upon confirmationof the handshake (block 132), a telemetry status indication may beoptionally provided to the user (block 135), e.g., telemetry statusindicator 86 as shown in FIG. 3 is activated.

[0077] Thereafter, upon confirmation of the handshake (block 132),signal strength (provided as described previously with reference to FIG.8A) based on gain of the uplink receiver 62 is compared to a referencethreshold. Such a comparison may be accomplished in any number ofmanners, and is not limited to any particular comparison circuit. Ifsuch a reference threshold is not met, then the user is not providedwith tactile feedback and the user recognizes the need to change theposition of the communication head 30. Further attempts to performtelemetry are then carried out (block 133). However, if the telemetrysignal strength satisfies, e.g., is greater than, the referencethreshold (block 134), then tactile feedback is activated (block 136)indicating to the user that a valid communication channel isestablished.

[0078] Thereafter, optionally, according to this embodiment, the tactilefeedback may be deactivated (block 138) after a predetermined time eventhough a valid communication channel still exists between theimplantable medical device 12 and the external communication device 15,i.e., the telemetry signal strength satisfies the reference thresholdrequirements. However, as described previously, handshake sequences arestill carried out periodically and continuously evaluate whether thelink continues to be valid over time. If a handshake sequence is notconfirmed after the tactile feedback has been deactivated (block 138),the communication link is no longer valid (block 140) and an alarmindicator (block 144) is activated to indicate to the user that the usermust reposition the communication head 30 (block 146) such that a validcommunication link can be re-established. If, however, continualconfirmation of the handshakes are completed, the user understands thatthe link is still valid and communication continues until telemetry iscompleted (block 142).

[0079] Another illustrative alternate embodiment of a head positioningmethod 150 is shown in FIG. 8C. In this embodiment, after a telemetrysession is initiated (block 151), telemetry is attempted (block 153).However, in this particular embodiment the signal strength based on thegain of the uplink receiver 62 is compared to a predetermined thresholdreference (block 152). If the signal strength is greater than thepredetermined threshold reference, then tactile feedback is activated(block 154) and the valid telemetry can be performed. However, if thesignal strength is not greater than the predetermined threshold, thenthe user must move the communication head 30 to another positionrelative to the implanted medical device 12 such that further telemetrymay be attempted (block 153) and further comparisons of signal strengthto a threshold can be carried out until the signal strength is greatenough to activate tactile feedback (block 154) such that the user knowsthat a valid communication channel is established between theimplantable medical device 12 and external communication device 15.

[0080] One skilled in the art will recognize that the implementation ofproviding tactile feedback to a user may be performed under the controlof software 84 of control circuitry 80 of the external communicationdevice 50 as shown in FIG. 3. As such, various techniques of using thetactile feedback can be implemented, including but clearly not limitedto controlling when tactile feedback is provided to a user based on anynumber of factors such as signal strength, error detection, cyclicredundancy checking, handshake confirmation, etc. For example, thedetermination of a valid channel using a handshake sequence may be usedalone or in combination with the use of signal strength to initiatetactile feedback, and signal strength may be used alone to determine thevalidity of the channel as compared to use of a handshake sequence.

[0081] Further, one skilled in the art will recognize that theseillustrative embodiments of determining the validity of thecommunication channel between the implanted medical device 12 and theexternal communication device 15 are given for illustration only andthat there are various other methods which may be used to determine avalid communication channel. The present invention is not limited to anyparticular validity determination method but is limited only to the useof tactile feedback to assist the user in positioning the communicationhead 30 relative to the implanted medical device 12 such that when avalid communication channel has been determined the user is effectivelynotified.

[0082] A more detailed diagram of one illustrative embodiment of aportion of an external communication device 300 for carrying out tactilefeedback for positioning of a communication head according to thepresent invention is shown in FIG. 4. The external communication device300 includes communication head 330 electrically connected to controlcircuitry 384. The communication head 330 includes therein an antenna364 coupled to transceiver circuitry 360 including downlink transmitter361 and uplink receiver 362. Generally, the uplink receiver 362 includesan automatic gain control amplification stage (not shown) which providesfor adjustment in gain based on signal strength, e.g., uplink and/ordownlink signal strength. A signal representative of the gain isprovided to a log amplifier 370 which provides as an output thereof asignal representative of the log of the signal strength. The log of thesignal strength is compared to a reference strength 373 as generallyillustrated by comparator circuitry 372. The tactile feedback generationdevice 374 is controlled by comparator circuitry 372. The comparatorcircuitry 372 has applied thereto a threshold reference 373 which isused for the comparison to the output of log amplifier 370representative of the gain of uplink receiver 362, and has appliedthereto an optional status indication 378.

[0083] Optional status indication 378 is controlled via controllercircuitry 384 which is also used in controlling the handshake betweenthe external communication device 300 and an implantable medical device12. When valid telemetry is detected per the handshake, optional statusindication 378, e.g., an LED, may be used to indicate to the user that atelemetry channel has been validated. Further, an enable signal isprovided to the comparator circuitry 373 upon occurrence of a confirmedhandshake such that only if the handshake is confirmed can tactilefeedback be performed. As such, even if the handshake is confirmed, itis not certain that the placement of the communication head 330 isoptimum for the telemetry link. Therefore, the log of the strengthsignal output from log amplifier 370 is provided to comparator circuitry372 for comparison to a threshold level 373. In this embodiment, onlyupon the strength signal meeting the threshold reference 373 is tactilefeedback device 374 activated.

[0084] It will be recognized that various threshold levels may be usedfor comparison with the output of the log amplifier 370 such thatvarious optional indication devices 376 may be activated. For example,and as further described below with reference to FIG. 5, an array ofLEDs may be used to visually indicate to a user the strength of thetelemetry signal. Likewise, the tactile feedback generation device 374may be controlled by the strength signal, e.g., the frequency ofvibration of the tactile feedback generation device 374 may be variedaccording to the strength of the telemetry signal.

[0085]FIG. 5 shows one illustrative embodiment of a portion of anexternal communication device 400 similar to that of FIG. 4 showing theuse of an array of LEDs 474 in combination with tactile feedback. Asshown therein, the log amplifier 470 receives as its input a signalrepresentative of the gain of the uplink receiver and provides an outputrepresentative of the log of the signal strength to driver circuitry472. Driver circuitry 472 is configured to drive an array of LEDs 474 asa function of the signal representative of the log of the signalstrength output from the log amplifier 470. For example, with a lowerstrength signal, only a single LED of the array 474 may be lit while asthe strength signal is increased, more LEDs may be lit.

[0086] As further shown in FIG. 5, tactile feedback generation device476 may be coupled to any point of the LED array such that tactilefeedback may be provided to the user by the generation device 476 uponactivation of a certain number of LEDs of the array 474. For example, itmay be desired that tactile feedback be provided to the user uponillumination of three LEDs corresponding to a certain signal strength.

[0087] The tactile feedback generation device 90, as shown in FIG. 3,and the tactile feedback generation devices as described with referenceto the other figures, may be provided in any number of manners. Forexample, as shown in FIG. 6, tactile feedback generation device 90 isprovided by control of a vibrating motor 91 which is mechanicallycoupled to the housing 31 of the communication head 30 so as to impartmotion or vibration to the communication head 30. For example, variousvibrating motors have been used in the paging industry such as describedin U.S. Pat. No. 4,794,392 to Selinko, entitled “Vibrator Alert Devicefor a Communication Receiver.” The vibrating motor 91 is controlled by acontrol signal 92 applied to a voltage regulator 93 which turns thevibrating motor 91 on and off. When the vibrating DC motor begins tovibrate, the user is provided with information regarding the positioningof the communication head 30 relative to the implanted medical device 12as described herein.

[0088] It will be recognized that other forms of generating tactilefeedback may also be used. For example, piezoelectric devices may beactivated to provide for vibration, an electric solenoid may beactivated for providing vibration, or a relay contact may be chatteredto also provide for vibratory or tactile feedback. As such, one skilledin the art will recognize that any number of vibration devices may beemployed in accordance with the present invention such that tactilefeedback may be used to indicate the validity of a communication channelbetween the external communication device 15 and the implanted medicaldevice 12.

[0089] All patents and references cited herein are incorporated in theirentirety as if each were incorporated separately. This invention hasbeen described with reference to illustrative embodiments and is notmeant to be construed in a limiting sense. As described previously, oneskilled in the art will recognize that various other illustrativetechniques for using tactile feedback in the positioning of acommunication head relative to an implantable medical device may beimplemented according to the present invention. Various modifications ofthe illustrative embodiments, as well as additional embodiments of theinvention, will be apparent to persons skilled in the art upon referenceto this description.

What is claimed is:
 1. An apparatus for indicating the relative signalstrength for a telemetry system when said telemetry system communicatesinformation between an external device and an implantable medicaldevice, comprising: an external transceiver unit coupled to an externaldevice; an internal transceiver unit coupled to an implantable medicaldevice; indicator means coupled to said external transceiver unit forcontinuously providing a first tactile indication of relative signalstrength of the external transceiver unit and the internal transceiverunit, wherein said tactile indication has a common frequencycharacteristic and said tactile indication has a greater magnitude for arelatively high signal strength than for a relatively low signalstrength.
 2. An apparatus according to claim 60, wherein a secondtactile indication is provided whenever the relative signal strengthdecreases below a predetermined lower threshold value and said secondtactile indication has a dominant frequency characteristic differentthan the common frequency characteristic of said first tactileindication.
 3. An apparatus according to claim 60, wherein saidindicator means is coupled to a hand-held communication head of saidexternal device or a compact member adapted to be manually coupled to auser and also to said external device.
 4. An apparatus according toclaim 61, wherein said indicator means further comprises a third tactileindication provided upon successful completion of a handshake protocolsequence between the external device and the implanted device, andwherein said third tactile indication has a dominant frequencycharacteristic different from the first tactile indication and saidsecond tactile indication.
 5. An apparatus according to claim 63,wherein said indicator means further comprises a fourth tactileindication provided during operation of the handshake protocol sequencebetween the external device and the implanted device and wherein saidfourth tactile indication has a dominant frequency characteristicdifferent from the first tactile indication, the second tactileindication, and the third tactile indication.
 6. An apparatus accordingto claim 62, wherein said indicator means operates pursuant to acomputer control system and further comprises at least a one of thefollowing: a vibrating motor; an electrical solenoid; an electricalrelay contact; or a piezoelectric device.
 7. An apparatus according toclaim 62, wherein in lieu of continuously providing said first tactileindication the indicating means provides said first tactile indicationfor a predetermined period of time and then ceases providing said firsttactile indication upon expiration of said predetermined period of time.